Spurs, also called spurious emissions and/or spurious signals, are signals at arbitrary frequencies wherein these frequencies do not belong to the carrier signal (desired signal) having a certain frequency. Accordingly, harmonics of that carrier signal having frequencies at an integer multiple of the frequency of the carrier signal can be considered as specific spurs. Further, oscillations and/or mixing terms also correspond to spurs wherein these spurs have frequencies at a non integer multiple of the frequency of the carrier signal. Generally speaking, spurs are signals having unwanted frequencies.
Further, the amplitudes of the spurs are small compared to the amplitude of the fundamental, namely the carrier signal. Thus, the amplitudes of the spurs are usually near the noise floor level of the signal received which impairs the measurement accuracy of the spurs as the resolution has to be very high in order to resolve these spurs.
In the prior art, different techniques are known to search for spurs in a signal received in order to identify the locations of the spurs in a frequency-domain diagram, in particular their frequencies. As already mentioned above, the frequencies of the spurs are not known aside from the frequencies of the (also unwanted) harmonics being integer multiples of the frequency of the signal received. Thus, the whole frequency range of the signal received is typically scanned with high sensitivity in order to determine the frequencies of the spurs due to their low amplitudes. The high sensitivity scan is established by using narrow resolution bandwidths (RBW) while sweeping across the whole frequency range of the signal received. This measurement is also called radio frequency sweep. However, the time needed for scanning the whole frequency range is very high when using a narrow resolution bandwidth. Nevertheless, the narrow resolution bandwidth is required in order to resolve the spurs having amplitudes being close to the noise floor level.
Accordingly, there is a need for searching a spur in a signal received in an efficient and fast manner.